An input/output (I/O) and control system for long distance communications and industrial applications having a bus and protocol for communications between field devices and a channel generator for monitoring and control of the field devices. The channel generator produces an offset square wave of configurable frequency on the bus, and sends a synchronization pulse of selected duration at the start of each bus scan cycle in a pulse train cycle to reset counters in the field devices before the bus scan cycle is repeated, to ensure field devices are synchronized, transmitters transmit on the correct channel, and receivers sample the pulse cycle at the correct time. Changing the synchronization pulse length increases bandwidth for shorter, less noisy and more stable systems and inversely decreases bandwidth for increased noise immunity and distance for longer, noisier and less stable systems.
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2. The method of claim 1, wherein the pulse train is a periodic waveform comprising instantaneous transition between the high voltage level and the low voltage level.
3. The method of claim 1, wherein pulse train has configurable frequency.
4. The method of claim 3, wherein the pulse train is an offset square wave with configurable frequency.
5. The method of claim 3, wherein the configurable frequency is dynamically configurable by the control unit during operation of the bus.
6. The method of claim 1, wherein the bus scan cycles comprise dual scan bus cycles having alternating A and B scan cycles where each A scan cycle and each B scan cycle comprises the selected number of I/O channels and its corresponding synchronization pulse.
7. The method of claim 1, wherein the pulse train is an offset square wave with configurable frequency, and comprises a selected number of cycles that are assigned to a corresponding number of the I/O channels and that are generated by the control unit.
8. The method of claim 7, wherein the selected number of I/O channels is configured in the control unit.
9. The method of claim 1, wherein the pulse train is an offset square wave and the high voltage level is between 12 VDC and 48 VDC and the low voltage level is between 2 VDC and 9 VDC.
10. The method of claim 1, wherein each of the plural devices is assigned to a corresponding one of the I/O channels in each of the bus scan cycles and has a counter, and the plural devices each reset their counter in response to the synchronization pulse to ensure that the plural devices transmit and receive on their corresponding I/O channels and that the control unit samples the pulse train at a correct pulse corresponding to a selected one of the plural devices.
11. The method of claim 1, wherein the synchronization pulse is generated al the high voltage level for different respective durations of time corresponding to different channel bandwidths.
12. The method of claim 1, wherein the high voltage level portions in the cycles of the I/O channels in the bus scan cycles can vary in at least one of duration within a cycle, and start of a rising edge of the high voltage level portion within a cycle, depending on whether the cycles are pulse width modulated as a mark or a space, the synchronization pulse is at the high voltage level for a selected duration of time depending on the channel bandwidth, and detection of the synchronization pulse employs a detection window having a range between the duration of the synchronization pulse and a mark and the duration of synchronization pulse and a space for detection of the synchronization pulse regardless of whether the last one of the I/O channel has a mark or a space.
13. The method of claim 1, wherein an I/O channel comprises one of the cycles.
14. The method of claim 1, wherein an I/O channel comprises a designated plural number of the cycles.
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November 28, 2016
August 30, 2022
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